Makefile: Remove usage of deprecated Python "has_key" method
"has_key" is a deprecated dictionary method in Python 2.6+.
Simplify the sys.path manipulation for installed scripts by
passing a default value to os.getenv() that takes a default
value to be used when the environment variable is missing.
SCRIPT_PYTHON is currently empty but this future-proofs us.
It also fixes things for users who maintain local git forks
with their own SCRIPT_PYTHON additions.
Old code replaced the first element of sys.path[] which is
typically '' (i.e. import library files relative to the script).
It is safer to prepend the extra library path instead.
Signed-off-by: David Aguilar <davvid@gmail.com>
Acked-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>